Electrocoatacure process and paint binders therefor



ELECTROCOATACURE PROCESS AND PAINT BINDERS THEREFOR Filed Sept. 7, 1967March 17, 1970 s rrH ETAL 2 Sheets-Sheet 1 V N QRL 7 Tami ER 6 5724MMarch 17, 1970 A. G. SMITH ET AL ELECTROCOATACURE PROCESS AND PAINTBINDERS THEREFOR Filed Sept. 7, 1967 2 Sheets-Sheet Z F/G. Z

United States Patent 3,501,391 ELECTROCOATACURE PROCESS AND PAINTBINDERS THEREFOR Arthur G. Smith, Livonia, and Allen H. Turner, Ann

Arbor, Mich., assignors to Ford Motor Company, Dearborn, Mich., acorporation of Delaware Continuation-impart of application Ser. No.583,885, Oct. 3, 1966. This application Sept. 7, 1967, Ser. No. 666,338

Int. Cl. B01k 5/02; C23b 13/00 US. Cl. 204181 21 Claims ABSTRACT OF THEDISCLOSURE A method for coating wherein a film-forming, polymerizable,organic coating material is electrodeposited upon an electricallyconductive object immersed in an aqueous medium and the resultantcoating polymerized on said object by ionizing radiation beforesignificant post deposition dehydration of said film is effected.

This application is a continuation-in-part of our copending applicationSer. No. 583,885 filed Oct. 3, 1966, and now abandoned.

This invention relates to a novel method for coating wherein afilm-forming, polymerizable, organic coating material iselectrodeposited upon an electrically conductive object immersed inaqueous medium and the resultant coating polymerized on said object byirradiation in gaseous medium. This invention further relates to novelcoating materials for use in such method.

In the method of this invention, 'an olefinically unsaturated coatingmaterial, at least a major proportion of which is a carboxylic acidresin ionizable in aqueous solution of water-ionizable amino compound,is dispersed in an aqueous solution of amino compound, the resultantionized resin is electrodeposited upon an electrically conductiveworkpiece moving through the bath by providing a difference ofelectrical potential between such workpiece and another electrode incontact with the bath, the resultant coated workpiece is removed fromthe aqueous medium into a gaseous medium and the freshly depositedcoating is polymerized upon the surface of such workpiece with a beam ofpolymerization effecting electrons to a tack-free, durable, surfacecoating.

The exact nature and interrelation of the electrical, chemical, physicaland electrochemical mechanisms of deposition, reaction and dehydrationassociated with electrically induced deposition of polycarboxylic acidresin are not fully understood although the phenomena ofelectrophoresis, electro-endosmosis, electrochemical conversion, etc.,have been advanced by way of explanation. Such understanding, however,is not required to appreciate the unique advantages demonstrated indurable, tenacious, continuous coatings of quality finish that areobtainable via electron induced polymerization of freshlyelectrodeposited coating.

The instant resins have a relatively high molecular weight and can beformulated to be characterized in that they deposit to form a continuousfilm of high specific resistance and of essentially even depth. Suchfilms are "ice essentially electrically irreversible under theconditions of coating, i.e. by current reversal. However, little isknown as to the resultant orientation of electrodeposited resin or resinand monomer and the physio-chemical conditions thereof in freshlydeposited film. Thus, full explanation of the particular suitability ofsuch films for electron induced polymerization is not readily available.Aside from the observable efficiences and qualities of the instantprocess, other advantages accrue from the complementary nature of thesteps therein, each acting in cooperation with those properties of theother which distinguish the same from other methods of deposition andpolymerization. For instance, electron induced polymerization isextremely rapid, a matter of seconds as opposed to a plurality ofminutes in conventional oven cure, and, while providing great savings intime and space, this characteristic of the process also presentsproblems in effecting cure without leaving areas of undercure orovercure. Opportunity for uneven cure with depth is reduced if the filmis of even depth. Electrically induced deposition in accordance with themethod of this invention is characterized by being selfleveling as aresult of the growth of resistance with film deposition. Further, inconventional processes for applying paint, volatile solvents arecommonly employed. In slow curing methods, the escape of such solventspresents no particular problem. With electron induced polymerization,this can result in the remnants of broken gas bubbles being solidifiedin place with resultant unsightly finish. The water-dispersible,electrodepositable paints used in the instant method can be, andpreferably are, free of solvents that volatilize in significantquantities or at significant rates during the polymerization step. Stillfurther, the energy released to a coating in electron inducedpolymerization can be controlled within extremely narrow limits andpolymerization can be effected without significant temperature increase.This broadens the scope of electrically induced deposition coating bypermitting the coating of electrically conductive products which areheat degradable and the formulation of electrodepositable coatingmaterials which would be unsuitable for use with slower, hightemperature cures.

The above-mentioned and other advantages of this invention will becomeapparent by reference to the following description taken in conjunctionwith the accompanying drawings, in which:

FIGURE 1 is a schematic assembly view of one embodiment of equipmentwhich may be used to carry out the method of this invention;

FIGURE 2 is a partial schematic illustration of one embodiment of one ofthe two electron-discharge devices shown in FIGURE 1;

FIGURE 3 is a perspective view of one embodiment of a combinationwindow-support grid and heat sink which forms a part of the device shownin FIGURE 2;

FIGURE 4 is a sheet of metal foil which serves as the electron window ofthe device shown in FIGURE 2;

FIGURE 5 is a perspective view of an apertured window-retaining memberwhich frames the electron window of FIGURES 2 and 3 and holds suchwindow in contact with the window-support grid and heat sink of FIGURE3; and

FIGURE 6 is a view taken along line 66 of FIG URE 1.

Referring now to FIGURE 1, a reel support stand 11 supports reel 13.Reel 13 formed of a suitable nonconductor, e.g. wood, plastic, etc., isrotatably mounted on stand 11 and carries a metal sheet stock 15. Uponbeing unwound from reel 13, the sheet stock 15 passes over idler 17which may be the same as or of different design with respect to theidler of FIGURE 6 which is hereinafter described. Idler 17 is rotatablymounted upon shaft 19 which in turn is supported by upright supportmember 21. Shaft 19 is a nonconductor and idler 17 is electricallyinsulated from ground. Sheet stock 15 passes under brush or rollercontact 23. Contact 23 is supportedby and in electrical contact withmetal shaft 25. In a first embodiment, contact 23 is rotatably mountedon shaft 25. In a second embodiment, contact 23 is fixedly secured toshaft 25. Shaft 25 is supported by horizontal support member 27. Supportmember 27 is a nonconductor and is supported by upright support member21. In a first embodiment, shaft 27 is a hollow shaft, a portion ofshaft 25 extends into shaft 27 and is rotatably supported therein. In asecond embodiment, shaft 25 is fixedly secured to the end of shaft 27.

After passing in electrical connection with contact 23, sheet stock 15dips into an aqueous bath 29, a dispersion of alpha-beta, olefinicallyunsaturated, carboxylic acid resin and amino compound as hereinafterdescribed. Bath 29 is retained in a coating tank 31 which serves as thegrounded cathode of an electrodeposition cell. Tank 31 is in electricalcontact with conductor 33 which in turn is in electrical contact with adirect current electrical power source 35. Also in electrical contactwith power source 35 is conductor 37 which in turn is in electricalcontact with metal shaft 25 via switch 39 and conductor 41. Thus, anelectric circuit is established which includes sheet stock 15, contact23, bath 29, grounded tank 31, conductor 33, power source 35, conductor37, switch 39, conductor 41, and shaft 25.

A difference of electrical potential is maintained between sheet stock15 and tank 31 that is in excess of the threshold deposition voltage ofthe resin employed. As used herein, the terms threshold depositionvoltage or threshold voltage refer to the minimum voltage at whichdeposition of an electrically resistant film of the given resin isinitiated. This will vary somewhat with the resin employed and/ or thecomposition of the resin-amino compound comprising the dispersion. Ahigh threshold deposition voltage is characteristic of a more stabledispersion. This minimum voltage will ordinarily be above 5 volts andbelow about 20 volts. However, for practical residence times for mostindustrial coating operations, a voltage above about volts will berequired. More commonly, this voltage will be in the range of about 100to about 250 volts. An upper limit on this difference of potential isdictated by the potential at which the deposited film will rupture ifmaintained throughout the bath residence period. This will also varywith the given resin but will ordinarily be below about 500 volts. Inthe pre ferred embodiments, at least the major proportion of the ilm iselectrically irreversible under the conditions of :oating.

The sheet stock 15 emerges from bath 29 hearing a :ontinuous,resin-comprising coating of substantially even iepth. Theresin-comprising coating at this point in the qrocess has not been curedand is relatively easily marred y physical contact. This coating shouldbe handled as ittle as possible prior to polymerization.

In certain embodiments, however, it will be found ad- Iantageous torinse the coating after it emerges from the ath to remove from thesurface of the coating loosely lssociated or adhered coating materials.Where such need :xists, the freshly coated sheet stock may be passedhrough a rinsing zone wherein the coated surface is conacted by waterspray or shower.

In accordance with the method of this invention, the =lectrodepositedfilm is subjected to polymerization effecting radiant energyimmediately'after its formation, i.e. before significant post depositiondehydration is effected. The polymerization will ordinarily be effectedwithin a time ranging from a few seconds to a few minutes,advantageously less than 10 minutes, and preferably less than 1 minute.

After the coated sheet stock 15 leaves the coating bath 29, it passesover idler 43, one embodiment of which is shown in greater detail inFIGURE 6. Idler 43 is rotatably mounted via bearings 45 and 47 withinand upon idler support stand 49. Idler 43 is a reel-like structureconsisting of a central shaft 43-1 which extends through and rotatesupon bearings 45 and 47, tubular support member 43-2 fixedly secured toshaft 43-1 and through which shaft 43-1 passes, circular support members43-3 and 43-4 fixedly secured to support member 43-2 at opposite endsthereof. Circular support members 43-3 and 43-4 have sloping surfaces43-5 and 43-6, respectively, against which the edges of sheet stock 15ride as it is pulled over idler 43 causing the idler to rotate. Idler 43is a nonconductor and insulates sheet stock 15 from ground. Idlersupport stand '49 is adjustably movable along the longitudinal axis ofsheet stock 15 via slots 49-1 and 49-2 in base support 50.

After passing over idler 43, coated sheet stock 15 passes between a pairof electron emission units positioned within housing 51 which effectpolymerization of the coating electrodeposited on sheet stock 15 to atack-free state. An electron emission device suitable for this purposeand representative of the electron emission units within housing 51 isillustrated in FIGURES 2-5 inclusive and described in detail inconnection with the description of such figures.

After passing between the aforementioned electron emission units, sheetstock 15, with the coating thereon polymerized to tack-free state, iswound around take-up reel 73. Reel 73 is formed of a nonconductivematerial which insulates sheet stock 15 from ground. Reel 73 isrotatably mounted on reel support stand 75. Reel 73 has a central shaftmember 73-1 which is operatively connected with an electric motor 77.Motor 77 is in electrical connection with power source 35 via conductor79, switch '81 and conductor 83. Motor 77 is also in electricalconnection with ground.

When the desired amount of coated sheet stock is taken up on reel 73,the power to all circuits is shut off, sheet stock 15 is severed betweenhousing 51 and reel 73, reel 73 is removed from reel support stand 75, anew take-up reel is installed on reel support stand 75, sheet stock 15is affixed to the new reel and the process is again started.

While only two electron emission units are indicated in FIGURE 1, itwill be understood by those skilled in the art that the speed with whichthe sheet stock is moved through the polymerization zone can beincreased by increasing the number of electron emission units employedfor polymerization of the coating. Likewise the length of the coatingbath can be extended to allow for increased line speed therethrough.

Housing 51 is adjustably movable along a-line normal to the longitudinalaxis of sheet stock 15 via slots 51-1 and 51-2 in base support member51-3. Mounted on housing 51 is a control unit 53. Control unit 53 is inelectrical connection with ground, with power source 35 via conductor55, and with the cathodes of the electron emission units within housing51 via conductor 55-1. Housing unit 51 and the anodes of the electronemission units within housing 51 are in electrical connection withground via conductor 55-2. Control 53 is also in electrical connectionwith a master control unit, not shown, which may include electrically orelectronically actuated program ming means, via conductors 57 and 59.Control unit 53 is also in electrical connection with switch 39 viaconductors 61 and 63 and switch 81 via conductors 65 and 67.

Mounted on the side of housing 51 downstream with respect to the coatingbath and the polymerization zone is monitoring unit 69 adapted toconstantly monitor the surface of sheet stock 15. Monitoring unit 69 isin electrical connection with control unit 53 via conductor 71. It isalso in electrical connection with housing 51 and hence with ground.Monitoring unit 69 includes sensing means, e.g. photoelectric means, forconstantly monitoring the condition of the coating film on sheet stock15 as it passes from the polymerization zone, e.g. by measuring lightreflection therefrom, and means for transmitting a constant evaluationthereof to control unit 53. It will be understood that other monitoringmeans, or monitoring means otherwise positioned, may also be used, e.g.contact friction measuring means, thickness measuring means, etc.

Control unit 53 comprises conventional electrical and/ or electroniccomponents operatively connected including switching means foractivating and deactivating the electron emission units within housing51, voltage control means for varying the potential of the electronbeams employed in polymerization of the coating, transfer means foradjusting the spacing between electron emission units Within housing 51and sheet stock 15, means for receiving and effectuating programmedcontrol signals from a master control unit to control the polymerizationprocess, means to receive signals from monitoring unit 69 and terminatecurrent flow in all circuits when imperfect coating is detected and/ortransmit such signals to a master control uint, etc.

Referring now to FIGURE 2, there is shown a cutaway view of the lowerend of an electron-accelerator tube 100 comprising a main housing 101containing a cathode assembly 103. Cathode assembly 103 comprises acathode housing 105 having an elongated aperture 107 extending along amajor portion of its lower side. Positioned within housing 105 is a pairof spaced apart bus'bars 109 and 111 which hold between them inelectrical communication therewith a plurality of tungsten-wirefilaments 113 which serve as cathodes. Aperture 107 is of a size andconfiguration such as to direct a sheet of electrons emitted by thefilaments 113 to the window area. In embodiments employing a scannedbeam, a changing magnetic field is em- "conductor 55 shown in FIGURE 1.Conductors 115 and 117 are insulated from housing 101 and housing 105.The energy delivered to the negative leads 115 and 117 is controlled byconventional electrical control means, not shown, so that a slightdifference of electrical potential, e.g. volts, is maintained betweennegative leads 115 and 117 to establish a current through the filaments113.

A conductor 119 provides the positive lead and is in electricalconnection with housing 101 and with ground, i.e. via conductor 55-2 ofFIGURE 1.

Affixed to the bottom end of housing 101 by suitable fastener means,e.g. bolts, clamps, screws, etc., is a heat sink and window-support grid121. Grid 121 is shown in greater detail in FIGURE 3. In thisembodiment, grid 1211's of copper or aluminum or an alloy thereof andhas a centrally positioned, longitudinally extending aperture 123. Aplurality of cross members 125 are seated in slots 127 and extendedtransversely across aperture 123. Grid 121 also has a plurality ofthreaded holes 129, the purpose of which is hereinafter explained. Grid121 also has a peripheral groove 131 shaped to receive a conduit 133 forbringing a heat exchange fluid, e.g. water, into heat-exchangerelationship with grid 121.

Positioned below grid 121 is window-forming sheet 141, a thin metalsheet which may be of aluminum; an alloy of aluminum containing minoramounts of lithium,

titanium, beryllium, magnesium, and/or thorium; stainless steel, etc.Window-forming sheet 141 is shown in FIGURES 2 and 4 in enlargedthickness to facilitate its location and identification in the drawings.It is positioned so as to completely cover aperture 123 of grid 121 andextend on each side of aperture 123 a suificient distance to be securedacross grid 121 by window-retaining block 151. Window-forming sheet 141is in electrical communication with housing 101 and serves as an anode.Window-retaining block 151 is provided with a centrally positionedaperture 153 of essentially equal size and configuration as that ofaperture 123 and has a plurality of threaded holes 155. Aperture 153frames the window proper. The threaded holes 155 provide means forsecuring window-retaining block 151 to grid 121 so as to clampwindow-forming sheet 141 to grid 121. Windowretaining block 151,window-forming sheet 141, grid 121 and housing 101 are fastened togetheras hereinbefore described using, where necessary, suitable gaskets,sealing rings, etc., not shown, so as to form a vacuumtype seal of thelower end of the housing 101. Also shown in FIGURE 2 is a portion ofsheet stock 15 of FIGURE 1 passing through an electron beam from theelectron accelerator above described.

The polymerization effecting electrons are provided by acceleratingelectrons to high energy in an evacuated tube, i.e. tube 100, andpermitting the accelerated electrons to issue from the tube through anappropriate electron window such as the aforedescribed window-formingsheet 141 onto the coating to be polymerized. To provide area coverage,the electrons may be caused to issue from the tube in the form of asheet, and the object to be irradiated may be moved through the electronsheet. The electron-emission unit above described is merelyrepresentative of a number of such devices which are suitable for thispurpose. In one such device, electrons are accelerated as a narrow beamwithin an evacuated tube, and then a rapid scanning movement is impartedto the electron beam before it passes through the electron window andissues from the tube. In another such device, an electron beam isfocused into sheet form within the tube by a system of cylindricalelectron optics. See, for example, US. Patents 2,602,751 and 2,680,814.Where precise focusing is not essential, the electron-emitting cathodeor cathodes may simply be partially enclosed in a suitable housingwithin the tube which restricts and directs the the electron beam to theelectron window as in the emitter described and illustrated in thedrawings.

The main housing 101, the window-forming sheet 141, Wll'ldOW supportgrid 121 and window-retaining block 151 with suitable gaskets, fastenermeans, etc., enclose and define an essentially gas-tight emissionchamber Which is substantially gas-evacuated by conduit and pumpingmeans, not shown, e.g. to an air pressure as low as about 10* mm. Hg.The electron window-forming sheet 141 through which the electrons issuefrom the acceleration tube is a thin sheet of relatively light metal andshould be as thin as feasible, e.g. 0.0001 inch in order that theelectrons may pass therethrough with minimum loss of energy. On theother hand, window-forming sheet 141 must have a sufficient mechanicalstrength to withstand a pressure differential of about one atmospheresince the interior will be exposed to the evacuated emission chamber andthe exterior ordinarily will be exposed to atmospheric pressure.

The amount of beam current which can be transmit ed through the electronwindow is determined by the physical properties of the window and theenergy of the impinging beam. Part of the beam energy is inevitablygiven up in the form of heat while electrons are passed through thewindow. The grid 121 and window-retaining block 151 provide means forheat exchange with the window. Conduit 133 provides means for additionalheat transfer via the circulation of a suitable coolant therethrough.The spacing of the grid components represents a compromise between theadvantages of maximum physical support and heat absorption on the onehand and the advantages of minimizing interception of electrons passingbetween cathode and window-forming sh et 141 which serves as an anode.Other electron accelerator designs are described by A. J. Gale in US.Patent 2,722,620 and by W. D. Coolidge in US. Patent 1,907,507.

While the illustrated embodiment of the invention is one wherein thework to be coated is sheet material, it will be understood that theworkpiece may be a Series of individual objects which pass through thecoating bath suspended from an overhead conveyor. In such an embodiment, the positions of the electron acceleration units would bemodified in accordance with the shape and size of the workpiece, e.g. asby lateral displacement from the path of the conveyor-supported andfreshly coat d workpiece. It will also be understood that where the workis sheet material, the means for feeding, conveying, charging andcollecting the sheet material may be modified in a variety of ways andstill perform the functions of the corresponding means illustrated.

Referring now specifically to the coating material, painting byelectrically induced deposition is herein meant to include thedeposition of finely ground pigment and/or filler in the binder, i.e.the ionizable resin or polymer or the ionizable resin and vinyl monomermix, the deposition of binder without pigment and/or filler or havingvery little of the same, but which can be tinted if desired, and thedeposition of other waterreducible surface coating compositionscontaining the binder which might be considered to be broadly analogousto enamel, varnish, or lacquer bases, and the coating material for suchdeposition is herein termed a paint. Thus, the binder, which isconverted to a water-resistant film by the electrodeposition andultimately converted to a durable film resistant to conventional serviceconditions by electron initiated polymerization, can be all or virtuallyall that is to be deposited to form the film, or it can be a vehicle forpigmentary and/or mineral filler material and/or other resins on whichit exerts the desired action for depositing the film.

In one preferred embodiment, the binder comprises a polycarboxylic acidresin having alpha-beta, olefinic unsaturation and vinyl monomers. Thepercentage of vinyl monomers advantageously is above about 1 and belowabout 15, preferably above about 7 and below about 14.5, more preferablyabout 9 to about 14 percent by weight of the organic binder.

The carboxylic acid resin is characterized in having a molecular weightabove about 1,000, advantageously in the range of about 2,000 to about20,000 where the resin is a polyester type resin. With acrylic or othervinyl resins, the molecular weight is advantageously above about 5,000,e.g. in the range. of about 5,000 to about 50,000 or higher. The resinis further characterized in having about 0.5 to about 3.0, preferablyabout 0.8 to about 2.0, alpha-beta olefinic unsaturation units per 1,000units molecular weight, an acid number above about 30, e.g. to 300,commonly to 120, and an electrical equivalent weight in the range ofabout 1,000 to about 20,000, preferably 1,000 to 3,000. The resinsemployed herein are characterized in deposition behavior in that theirdeposition is essentially directly proportional with the direct currentpassing through the bath. This results from the fact that a film of highspecific resistance builds with deposition. The resins employed in themethod of this invention deposit as a film that is (1) substantiallyuniform in thickness providing the workpiece is of such configurationthat substantially equal electrical inducement to coating can beachieved at all surfaces thereof for a significant period of time duringthe coating process, (2) essentially Water insoluble, (3) of highspecific resistance, (4) terminates at a maximum thickness for a givenvoltage, and (5) is quickly polymerizable by an electron beam totack-free state. Electrically induced deposition of polycarboxylic acidresins which meet the first four of these properties is disclosed by A.E. Gilchrist in U.S. Patent 3,230,162. So far as it is known, the binderresins heretofore employed for electrically induced deposition fromaqueous bath have not been suitable for rapid cure by electron inducedpolymerization.

Radiation induced polymerization, including the use of an electron beamas the source of radiant energy, is exemplified in the art by US.Patents 3,247,012; 3,188,229; 3,188,228; 3,188,165; 3,170,892;3,146,146; 3,137,674; 3,131,139; 3,107,206; 3,088,791; 3,077,420;3,077,419; 3,077,418; 3,077,417; 3,075,904; 3,013,895; 2,999,056;2,964,456; 2,956,904; 2,955,953; 2,921,006; 2,904,481; and 2,900,277.80far as it is known, the materials described in this group of patents andother materials heretofore polymerized by radiant energy have not beenemployed or eificiently employable as water-dispersible,electrodepositable coating materials.

The novel paint binders of this invention are characterized by'beingboth electrodepositable in the manner of the resins of theaforementioned Gilchrist patent and electron polymerizable by themethods set forth in the other patents hereinbefore listed.

Referring now specifically to bath 29 the aqueous dispersion willcontain between about 0.5 and about 35 percent by weight of thedispersed binder material, advantageously about 3 to about 12' percent.The water soluble amino compound employed as a dispersal assistant ispresent somewhat in excess of the amount necessary to effect intimatedispersion of the resin and to impart anionic polyelectrolyte behaviorto the same. The optimum quantity of amino compound to be employed willvary with the acid number of the resin. If the resultant pH issufficiently high, the bath will absorb CO from the atmosphere unless acontrolled atmosphere is employed. The concentration of the aminocompound or compounds will also affect the electrical resistance of thebath and is deemed excessive when the bath resistance fallssubstantially below about 500 ohm-cm. The proportion of amine used is inexcess of the minimum amount necessary for imparting anionicpolyelectrolyte behavior to the particular binder resin or resin mixturein the bath. Concentrations of about 1.5 to about 5.3 times such minimumhave been found suitable. Specific resistance of the bath isadvantageously between about 700 and about 1000 ohm-cm. Higher bathresistance will result in a thinner coating at a given potentialdifference and vice versa. A bath of pH as low as about 5 and as high asabout 10 can be used. Advantageously the pH is between about 6.5 andabout 85, preferably between about 7.0 and about 7.5.

Bath viscosity is advantageously maintained below about 30 times theviscosity of water. Bath temperatures in the range of about 15 to about50 C. facilitate maintenance of bath stability and inhibit intrabathpolymerization. I

The term water soluble amino compound as herein employed includesammonia and water soluble amines. Ammonia is less advantages in thisprocess for partially neutralizing the acid resin or resin mixturebecause it is highly volatile at operating temperatures and small additions of it can cause comparatively large changes in the pH of the bath.The amines used are amines that are soluble in water at 20 C. to theextent of at least about 1% basis weight of solution and include hydroxyamines, polyamines and monoamines such as: monoethanolamine,diethanolamine, triethanolamine, N-methyl ethanolamine, Naminoethylethanolamine, N methyl diethanolamine, monoisopropanolamine,.diisopropanolamine, triisopropanolamine, poly-glycol amines such asHO(C H O) C H NH hydroxylamine, butanolamine, hexanolamine,methyldiethanolamine, octanolamine, and alkylene oxide reaction productsof monoand polyamines such as the reaction product of ethylene diaminewith ethylene oxide or propylene oxide, lauryl amine with ethyleneoxide, etc., ethylene diamine, diethylene triamine, triethylenetetramine, hexamethylene tetramine, tetraethylene pentamine, propylenediamine, 1,3 diamino-propane, imino-bis-propyl amine, and the like, andmono-, diand tri-lower alkyl (C -C amines such as mono-, diand tri-ethylamine.

To supplement the carboxylic acid resin in the bath as operationscontinue, additional binder concentrate composition is addedcontinuously or incrementally. This concentrate optionally containspigment. For ease of dispersion, the concentrate is advantageously inthe form of a concentrated aqueous dispersion containing on a pigmentand filler-free basis, about 50-95 percent by weight of polycarboxylicacid resin (straight or extended) and about 1-10 percent by weight watersoluble amino compound based on the weight of the polycarboxylic acidresin, and the balance water.

The terms radiation, ionizing radiation, and radiant energy as employedherein mean radiation having a minimum energy of, or equivalent to50,000 electron volts. The preferred method of curing films of theinstant paint binders upon the substrates to which they have beenapplied is by subjecting such films to a beam of polymerizationeffecting electrons which at its source of emission, i.e. upon emergingfrom the electron window, is within the range of, equivalent to, about100,000 to about 450,000, preferably about 200,000 to about 350,000electron volts.

By varying the space between the electron source and the film inrelation to the potential of the beam, the difference in polymerizationrates with depth can be minimized. Within the aforementioned range ofpotentials, it is preferred to maintain a minimum voltage of about25,000 volts per inch separation between emitting means and the film tobe cured. In accordance with this process, the distance between emittingmeans and the film on the workpiece can be varied from about 2 feet tothe minimum clearance compatible with the contours of the workpiece.Ordinarily, a space range of about 2 to about 18 inches will be mostefiicient. The correlation of space distance with emission potentialbecomes increasingly important with an increase in either space distanceor film depth. At the closer spacings, voltages in the lower portion ofthe range can be successfully employed. Higher voltages permissiblethroughout this range becomes necessary at the greater distances toprovide the desired uniformity of polymerization rates with depth. Whenoperating in the range of about 200,000 to 300,000 electron volts,spacings in the range of about 2 to about 12 inches are preferred.

Although the tolerance to overexposure will vary somewhat with filmcomposition, the time required to effect substantially completepolymerization of the film at its maximum depth ordinarily should not begreater than twice the time required to polymerize the most easilypolymerized portion of the film. Preferably, this time is less than 1.5times the period required to obtain the first polymerization. Thetemperature of the film should be insufiicient to cause significantevaporation of the most volatile component thereof both before andduring polymerization. Keeping within these limitations, dose rates inthe range of about 0.01 to about 15, preferably 0.1 to megarad/ sec.have been found suitable.

The term Rad. as employed herein means that dose of radiation whichresults in the absorption of 100 ergs of energy per gram of absorber,i.e. coating film.

The term acrylic monomer as used herein means an alpha-betamonounsaturated monocarboxylic acid or esters thereof and includes, butnot by way of limitation, acrylic acid, alkacrylic acids, e.g.methacrylic acid, monohydric alcohol esters of acrylic acid andalkacrylic acids, e.g. glycidyl methacrylate, 2-hydroxy-ethylmethacrylate, etc.

The acid number of resins without appreciable anhydride groups can bedetermined with KOH by the ASTM standard method 55554. If appreciableanhydride groups are present, the acid number can be determined byrefluxing a 1.52 gram sample of the portion of the resin for 1 10 hourwith 50 ml. of 0.5 N aqueous KOH and 25 ml. of pyridine, then backtitrating with 0.5 N HCl of a phenolphthalein end point.

The electrical equivalent weight of a given resin or resin mixture isherein defined as that amount of resin or resin mixture that willdeposit per Faraday of electrical energy input under the conditions ofoperation hereinafter set forth. For this purpose, the value of oneFaraday in coulombs is herein taken to be 107.88 (atomic weight ofsilver) +0.001118 (grams of silver deposited by one coulomb from silvernitrate solution) or 96,493. Thus, if 0.015 gram of coating, the binderpolycarboxylic acid resin moiety of which is by weight and the balanceof which is amino compound used to disperse it in the bath istransferred and coated on the anode per coulomb input to the process,the electrical equivalent weight of the resin is about 1303 or 0.015 0.9107.88+0.001118.

By way of further illustration, the electrical equivalent weight of aparticular polycarboxylic acid resin or resin mixture can be foundsimply and conveniently for typical process conditions standardized onas follows: a polycarboxylic acid resin concentrate is made up at 65.56C. (150 F.) by thoroughly mixing 50 grams of polycarboxylic acid resin,8 grams of distilled water and diisopropanol amine in an amountsufiicient to yield resin dispersion pH of 7.8 or slightly lower afterthe concentrate has been reduced to 5% by weight resin concentrationwith additional distilled water. The concentrate is then diluted to 1liter with additional distilled water to give 5% resin concentration inthe resulting dispersion. (If a slight insutficiency of the amine hasbeen used, and the dispersion pH is below 7.8, pH is brought up to 7.8with additional diisopropanol amine.) The dispersion is poured into ametal tank, the broadest side Walls of which are substantially parallelwith and 2.54 cm. out from the surface of a thin metal panel anode. Thetank is wired as a direct current cathode, and the direct current anodeis a 20 gauge, 10.17 cm. (4 inches) wide, tared steel panel immersed inthe bath 7.62 cm. (3.5 inches) deep. At 26.67 C. (80 F.) bathtemperature, direct current is then impressed from anode to cathode atvolts for 1 minute from an external power source, the current measuredby use of a coulometer, and the current turned off. The anode panel isremoved immediately, rinsed with distilled water, baked for 20 minutesat 176.67 C. (350 F.) and weighed. All volatile material such as waterand amine is presumed to be removed from the film for practical purposesby the baking operation. The difference between tared weight of thefresh panel and final weight of the baked panel divided by the coulombsof current used, times 107.88, divided by 0.001118 gives the electricalequivalent weight of the resin for purposes of this invention.

In another preferred embodiment, the polymerizable portion of the binderconsists essenitally of polymers which are homopolymerizable. Thus, inthis embodiment, the vinyl monomer component of the formulation can beomitted although it is within the scope of this invention to employpolymerizable monomers with these resins as in the previously describedembodiment. In this embodiment, the binder polymer has a molecularweight above about 250, at least 1 and preferably at least 2 dissociablecarboxyl groups per molecule, and at least 2 units of alpha-betaolefinic unsaturation per molecule. Advantageously, such units ofunsaturation are terminal with respect to the polymer when the latter isessentially linear and are present in the concentration range of about 2to about 4 of such units per 1,000 units molecular weight.

These polymers may comprise the sole component of a paint binder or beemployed in combination with other polymers and/or monomers with whichthey are co polymerizable by ionizing radiation. With a view to theintended end use and the presence or absence of other unsaturatedcomponents in the coating formulation, the molecular weight of suchpolymers may range upward from the aforestated minimum to an aveargemolecular weight of several thousand or more. In dispersing certainembodiments of these polymers in an aqueous bath and in theelectrodeposition thereof upon a conductor, it will be foundadvantageous to employ therewith a compatible organic solvent which,depending upon the desired end product, may either be removed byvolatilization prior to curing or retained as a plasticizer in the curedfilm. Such solvent will facilitate formation of a continuous andadherent film upon electrodeposition.

The polymers of this invention can be prepared by reacting a basepolymer having at least 2 functional groups per molecule, i.e. hydroxyl,amino, carboxyl, anhydride, mercapto, or epoxide groups, with an organiccompound having alpha-beta olefinic unsaturation, preferably di-, orpoly-, carboxylic acid or anhydride. Where the polymer iselectrodeposited the resultant polymeric product must contain sutficientionizable functional groups within its molecular structure to admit ofdisv persion in an aqueous bath and subsequent electrodep osition, e.g.dissociable carboxylic groups in the case of anodic deposition. Theseionizable functional groups may be originally present in theaforementioned base polymer or on the organic compound with which it isreacted. The illustrated products are linear copolymers with terminalalpha-beta olefinic unsaturation units.

This invention will be more fully understood from the followingillustrative examples.

EXAMPLE 1 A silicon-modified, polyester type, polycarboxylic acid resinis prepared from the following components:

Moles Grams Ml Maleic anhydride 0. 63 Tetrahydrophthalic anhydride 1. 61Neopentyl glycol 2. 48 Polysiloxane by weight) Xylene Hydroquinone Thepolysiloxane employed is a commercially available (Dow Corning Z-6018)hydroxy-functional, cyclic, polysiloxane having the followingproperties:v Y

Hydroxy content, Dean Stark:

The glycol, the polysiloxane and the xylene are added to a four neckliter flask, heated to a temperature of about 160 to about 165 C. forabout 2 hours while being stirred and under a nitrogen atmosphere. Thereaction mixture is cooled to about 125 to about 130 C., the maleicanhydride, the tetrahydrophthalic anhydride and the hydroquinone areadded and the temperature is increased slowly to about 190 to about 200C. which is maintained for about 3.5 hours and to an acid number ofabout 47.7. The heating is stopped, the xylene is stripped, and themixture is cooled to about 80 C. About 45.0 grams styrene and about 45.0grams methylmethacrylate are added. The acid number of this bindersolution is then determined to be about 43.4. This binder solution ishereinafter termed Binder A.

This mixture is placed in a ball mill and milled for approximately 38hours. This mill base is hereinafter termed Mill Base 1.

A- resin-monomer dispersion is prepared from the following components:

Grams Mill Base 1 13.8 Binder A 66.2 Diisopropanolamine 7.3 Distilledwater 312.7

The amine and water are blended in a high speed mixer. The mill base andthe binder are premixed and then poured into the vortex of the aqueousmixture of amine and water. The resultant mix is blended for 10 minutes.Blending is stopped for 5 minutes and then continued for 5 minutes.Blending is stopped for 20 minutes and then continued for 5 minutes.After 5 minutes, the dispersion is stirred with 400 grams of distilledwater. The resulting emulsion has about 10 wt. percent solids.

This emulsion is placed in a tank which serves as the cathode of anelectrodeposition cell. Steel sheet stock is coated by providing adifierence of electrical potential between the cathode and the sheetstock (anode) of about volts for about 1 minute.

The sheet stock is removed from the bath into a nitrogen atmosphere andthe essentially uniform and continuous coating thereon is polymerized totack-free state by passing the coated panel through an electron beam.The conditions of irradiation employed are as follows:

Voltage-275 electron kilovolts Current15 milliamperes Total dosage-10megarads Passes through beam2.

Line speed-10 ft. /min. Atmosphere-nitrogen Distance, electron window towork7 inches EXAMPLE 2 A paint is prepared, electrodeposited from anaqueous bath upon a metal panel and polymerized by an electron beam asin the previous example except for the differences hereinafter setforth.

To a reaction vessel are added the following materials:

Moles Grams (a) Methylmethacrylate (b) Ethylacrylate (c) Glycidylmethacrylate (d) Methacrylic acid (e) Xyle (f) Benzoyl peroxide" (g)Hydroquinone- The xylene is heated to C. under a nitrogen blanket andstirred continuously. The monomers (a), (b), and (c), the reactioninitiator (f) and the hydroquinone (g) are added to the xylene. Themonomers (a), (b) and (c) are added separately and incrementally over aperiod of about 3 hours. The charge is heated at 130 to 133 C. for about3 hours. The charge is cooled to about 50 C.

The methacrylic acid (d) is added to the charge and the temperature israised to 138 C. gradually and maintained until an acid number of about60 is obtained. The xylene is then removed.

The acrylic polymer thus formed is admixed with styrene andmethylmethacrylate in the same proportions as in the preceding example.

The voltage employed in electrodepositing the binder Potential295 kv.

Current-1 milliampere Atmosphere-helium Line speed6.5, 312 and 1.6cm./sec. Distance, emitter to panel-10 inches Passes through beam2Dose-2.5, 5 and megarads EXAMPLE 3 A polyester type, polycarboxylic acidresin is prepared from the following components:

Grams Fumaric acid 222.9 Tetrahydrophthalic'anhydride 925.1Trimetholpropane monoallyl ether 1477.2

The above materials are mixed with 250 ml. of xylene and 0.02%hydroquinone. The mixture is heated at 190 C. until 130 ml. of water isremoved and an acid number of about 50 is reached. The solvent isremoved with a stream of nitrogen gas and a yield of about 2486 grams isobtained. 1

Using a conventional blender, 300 ml. of water is mixed with 26 ml. of 1normal diisopropanolamine. Thirty (30) grams of the resin is slowlyadded and stirring is continued for 30 minutes. The resulting dispersionis diluted with water to 390 grams total weight. This material hasapproximately 0.9 alpha-beta olefinic unsaturation groups per 1,000units molecular weight.

Steel panels pretreated in a conventional zinc-phosphating process areused as anodes in an electrodeposition cell wherein the aforementioneddispersion serves as the electrolyte and its retainer, the coating tank,serves as the cathode. The immersed area of the anode is 37.4 cm. (5.2cm. x 7.2 cm.). The cathode-anode spacing is about 2 inches. A potentialdifference between anode and cathode of about 100 volts is applied forabout 1 minute and a resinous film of essentially uniform depth isdeposited. The initial current between anode and cathode is about 0.82ampere and this drops with increase of electrical resistanceattributable to the deposited film to about 0.07 ampere. This results ina deposition of about 0.218 gram of resin upon the panel with autilization of about 8.8 coulombs of charge or an electrical equivalentweight of The anode is removed from the bath and contacted with anelectron beam. The distance between the electron window and coated panelis about 12 inches. The atmosphere is air. Electron emission is at280,000 electron volts. The coating is subjected to a total dosage ofabout 40 magarads and a tack-free film is obtained.

This procedure is repeated except that a binder solution is prepared byadmixing styrene monomer with the resin prior to dispersion in the bath.Upon irradiation in like manner, it is found that a tack-free film isobtained with a dosage of about 10 megarads. The mixture employedcontains about 12% styrene and about 88% resin.

This procedure is repeated except that A of the styrene is replaced withmethylmethacrylate.

EXAMPLE 4 The procedure of Example 1 is successively repeated with theconcentration of binder in the coating bath adjusted to 0.5, 12, and 35percent by weight in separate runs.

EXAMPLE 5 The procedure of Example 1 is repeated with the electricalpotential employed in electrodepositing the binder reduced to 50 voltswith residence time for the workpiece in the bath extended to 3 minutes.

EXAMPLE 6 The procedure of Example 2 is repeated with the electricalpotential employed in electrodepositing the binder increased to 250volts.

EXAMPLE 7 The procedure of Example 1 is repeated with the potential ofthe electron beam reduced to about 150 electron kilovolts and line speedreduced to 2 feet per minute.

EXAMPLE 8 A polymer is prepared in the following manner:

(1) To a flask equipped with stirrer, dropping funnel, thermometer,condenser, and nitrogen inlet, is added at room temperature thefollowing ingredients:

Resin A3 13 .5 grams Itaconic anhydride214 grams Benzyl dimethyl amine10grams Dioxane-275 ml.

Resin A is an epoxy resin having an epoxy equivalent of 185-192, theresinous product formed by conventional reaction of epichlorohydrin andbisphenol A in the presence of caustic. This resinous product has thefollowing characteristics:

Average mol wt. 380 Equ valent hydroxyl content per 1,000 grams resin0.06 Equivalent weight, gins. resin to esterify mole acid Viscosity at25 C., poises -160 (2) The charge is heated in a nitrogen atmosphere atreflux temperature for 4 hours. Titration with aqueous NaOH indicatesthat all of the anhydride has reacted and that 50% of the theoreticalcarboxyl value of the anhydride remains.

(3) The solvent (dioxane) is removed by distillation followed by vacuumdistillation.

(4) A light amber colored resinous product, a viscous liquid, isrecovered.

An electrodeposition bath is formed by admixing 100 grams of product 50prepared with 200 ml. water and 26.8 ml. diethylarnine and stirringuntil a dispersion of the resin is obtained. This dispersion is furtherdiluted with water until 1 liter of bath is obtained. This liquid isthen employed as the bath of an electrodeposition cell in which themetal container of the bath serves as the cathode. A metal workpiece, aZinc phosphate-treated sheet steel, is immersed in the bath and employedas the anode of such cell. Electrodeposition of the dispersed resin uponthe anode is eifected by impressing a difference of electrical potentialbetween anode and cathode of about 32 volts for 1 minute. The averagedistance between anode and cathode is about 3 inches and the current atthe end of 1 minute is about 0.2 ampere. The area coated on each of thetwo major sides of the workpiece is about 6 square inches. The workpieceis removed from the bath and immediately rinsed with water.

The coating thus obtained upon the workpiece is polymerized to tack-freestate by passing the workpiece through a beam of polymerizationefiecting electrons. The following conditions are employed inarradiating the coated workpiece thus prepared:

Beam potential270 kv. Current1 milliampere Atmospherenitrogen Distance,emitter to workpiece-10 inches Dose12 megarads EXAMPLE 9 The procedureof Example 8 is repeated with the single difference that about 5 ml.xylene is added to the electrodeposition bath and electrodeposition iscarried out at a difference of potential of about 15 volts for 1 minute.

EXAMPLE 10 The procedure of Example 8 is repeated except that thepolymer is prepared in the following manner:

(1) To the reaction flask is charged 313 grams of resin A of Example 8and 175 grams of diethanolamine.

(2) This solution is maintained at 70 C. and 275 ml. dioxane are addedthereto over a period of about 3 hours.

(3) The reaction mixture is heated at reflux temperature for about 3hours.

(4) The resinous product obtained is recovered from the solvent andidentified as resin B.

(5) The resin B produced as above described is admixed with 428 grams ofitaconic anhydride and 500 ml. of dioxane under a nitrogen blanket. Thereaction is exothermic and the temperature rises to about 55 C. Thecontents of the reaction vessel are maintained at a temperature of about4050 C. overnight and the polymer thus obtained is separated from thesolvent.

An electrodeposition bath is prepared as in Example 8 with thedifferences being the use of the polymer produced above with sufficientdioxane added to provide a Gardner viscosity of about Z3.

Electrodeposition and electron initiated polymerization is then carriedout as in Example 8.

The term base polymer is employed in this application to include dimers,tri-mers, and tetramers as well as higher molecular weight polymers. Theterm dispersion as employed herein in relation to intimate dispersal ofpolymer with an aqueous coating bath is meant to convey the broadmeaning of such term, i.e. to include colloidal suspensions, emulsions,solutions, etc.

The foregoing examples are solely for purposes of illustration andshould not be considered as limitations upon the true scope of theinvention as set forth in the claims.

We claim:

1. A method for coating an electrically conductive substrate comprisingin combination the steps of (1) immersing said substrate in a coatingbath consisting of an aqueous dispersion of paint characterized in thatit is both electrodepositable from aqueous dispersion as an adherentfilm upon an anode immersed therein and polymerizable thereon byionizing radiation having energy at least equivalent to that of 50,000electron volts, said coating bath, on a pigment and particulatefiller-free basis, comprising an aqueous dispersion of an acidicfilm-forming binder, said acidic film-forming binder being selected from(al a. homopolymerizable, alpha-beta olefinically unsaturated resinhaving at least one dissociable carboxyl group per molecule, and

(b) an alpha-beta olefinically unsaturated resin having at least onedissociable carboxyl group per molecule and a crosslinkable amount ofvinylmonomers,

(2) electrodepositing a film of said binder upon the immersed substrateby employing said substrate as the anode of an electrodeposition celland providing a unidirectional electric current through said dispersionthat is quantitatively and directionally sufficient to effect depositionof a film of said binder upon said substrate by providing a difierenceof electrical potential between said substrate and a cathode that is (a)electrically negative in relation to said substrate,

(b) spaced apart from said substrate,

(0) in electrical contact with the aqueous phase of said aqueousdispersion, and

(d) in electrical connection with said substrate in 16 externalrelationship to said bath thereby completing an electrical circuit,

(3) transferring the resultant coated substrate from said aqueousdispersion into a gaseous medium within an irradiation zone,

(4) exposing the electrodeposited film in said irradiation zone toionizing radiation having energy at least equivalent to that of 50,000electron volts before substantial post deposition dehydration of saidfilm is effected, and

(5) continuing the exposure of said film to said ionizing radiationuntil said film is polymerized on said substrate.

2. A method of coating in accordance with claim 1 wherein said ionizingradiation is supplied in the form of an electron beam having averageenergy in the range of about 100,000 to about 450,000 electron volts.

3. A method for coating in accordance With claim 1 wherein saiddifference of electrical potential between said substrate and saidcathode is in the range of about 50 to about 500 volts.

4. A method for coating in accordance with claim 1 wherein said gaseousmedium is of reduced oxygen content relative to air.

5. A method for coating in accordance with claim 1 wherein theelectrodeposited film on said substrate is contacted with said ionizingradiation and polymerized within less than 10 minutes after its removalfrom said paint bath.

6. A method for coating in accordance with claim 1 wherein theelectrodeposited film on said substrate is contacted with said ionizingradiation and polymerized within less than 1 minute after removal ofsaid film from said coating bath.

7. A method for coating an electrically conductive sheet metal substratecomprising in combination the steps of (1) immersing a first portion ofsaid substrate in a paint bath consisting of an aqueous dispersion ofpaint characterized in that it is electrodepositable from aqueousdispersion upon an anode immersed therein as an adherent film ofsubstantially even depth which increases in electrical resistance withdepth and is polymerizable thereon by ionizing radiation having energyat least equivalent to that of 50,000 electron volts, said paint bath,on a pigment and particulate filler-free basis, comprising an aqueousdispersion of film-forming paint binder at least a major proportion ofwhich is acidic film-forming paint =binder, said acidic film-formingpaint binder being selected from (a) a homopolymerizable, alpha-betaolefinically unsaturated resin having at least one dissociable carboxylgroup per molecule, and

(b) an alpha-beta olefinically unsaturated resin having at least onedissociable carboxyl group per molecule and a cross-linkable amount ofvinyl monomers,

(2) electrodepositing a film of said paint upon the immersed substrateby employing said substrate as the anode of an electrodeposition celland providing a unidirectional electric current through said dispersionthat is quantitatively and directionally sufficient to eifect depositionof a film of said paint upon said substrate by providing a difference ofelectrical potential between said substrate and a cathode that is (a)electrically negative in relation to said substrate,

(b) spaced apart from said substrate,

(c) in electrical contact with the aqueous phase of said aqueousdispersion, and

(d) in electrical connection with said substrate in externalrelationship to said bath thereby completing an electric circuit,

(3) transferring said first portion of said substrate from said paintbath into a gaseous medium within wherein said difference of electricalpotential between said substrate and said cathode is above about 50 andbelow about 500 volts.

wherein said difference of electrical potential between said substrateand said cathode is in the range of about 100 to about 300 volts.

17 an irradiation zone while a second portion of said substrate isentering said paint bath,

(4) exposing the electrodeposited film on said first portion of saidsubstrate in said irradiation zone to ionizing radiation in the form ofan electron beam having average energy in the range of about 100,000 5to about 450,000 electron volts before substantial post depositiondehydration of said film is effected and while said second portion ofsaid substrate is immersed in said paint bath, and

(5) continuing the exposure of the electrodeposited film on said firstportion of said substrate to said ionizing radiation until the same ispolymerized.

8. A method for coating in accordance with claim 7 9. A method forcoating in accordance with claim 7 10. A method for coating inaccordance with claim 7 wherein said gaseous medium consists essentiallyof nitrogen.

11. A method for coating in accordance with claim 7 12. A method forcoating in accordance with claim 7 13. A method for coating anelectrically conductive substrate comprising in combination the steps of(1) immersing said substrate in a coating bath consisting of an aqueousdispersion of paint characterized in that it is electrodepositable fromaqueous dispersion upon an anode immersed therein as an adherent film ofsubstantially even depth which increases in electrical resistance withdepth and is polymerizable thereon by ionizing radiation having energyat least equivalent to that of 50,000 electron volts, said paint bath,on a pigment and particulate filler-free basis, comprising an aqueousdispersion of an acidic filmforming paint binder at least partiallyneutralized with water soluble amine and consisting essentially of a'minor component of vinyl monomers and a major component of analpha-beta olefinically unsaturated acid resin that deposits upon ananode immersed in said bath in direct proportion to direct electriccurrent passed through said bath between said anode and a cathode inelectrical contact with said bath, has acid number in the range of about30 to about 300, an electrical equivalent weight in the range of about1,000 to about 20,000, a molecular weight in excess of about 1,000, andabout 0.5 to about 3 alpha-beta olefinic unsaturation units per 1,000units molecular weight,

(2) electrodepositing a film of said binder upon the immersed substrateby employing said substrate as the anode of an electrodeposition celland providing a unidirectional electric current through said dispersionthat is quantitatively and directionally sufiicient to effect depositionof a film of said binder upon said substrate by providing a differenceof electrical potential between said substrate and a cathode that is (a)electrically negative in relation to said substrate,

(b) spaced apart from said substrate,

(0) in electrical contact with the aqueous phase of said aqueousdispersion, and

(d) in electrical connection with said substrate in externalrelationship to said bath thereby completing an electrical circuit,

(3) transferring the resultant coated substrate from said aqueousdispersion into a gaseous medium within an irradiation zone, q

(4) exposing the electrodeposited film to ionizing radiation in saidirradiation zone in the form of an electron beam having average energyin the range of about 100,000 to about 450,000 electron volts beforesubstantial post deposition dehydration of said film is effected, and

(5) continuing the exposure of said film to' said ionizing radiationuntil said film is polymerized on said substrate. I

14. A method for coating in accordance with claim 13 wherein said minorcomponent comprises about 1 to about 14.5 percent by weight of saidbinderand said major component comprises about 85.5 to about 99 percentby weight of same. 7

' 15. A method for coating in accordance with claim 13 wherein saidminor component comprises about 9 to about 14 percent by weight of saidbinder and said major component comprises about 86 to about 91 percentby weight of same.

16. A method for coating in accordance with claim 13 wherein theelectrodeposited film on said substrate is contacted with said ionizingradiation and polymerized within less than 1 minute after removal ofsaid film from said paint bath.

17. A method for coating in accordance with claim 13 wherein saidgaseous medium consists essentially of an inert gas.

18. A method for coating in accordance with claim 13 wherein saidgaseous medium consists essentially of an inert gas.

19. A method for coating an electrically conductive substrate comprisingin combination the steps of (1) immersing said substrate in a coatingbath consisting of an aqueous dispersion of paint characterized in thatit is electrodepositable from aqueous dispersion upon an anode immersedtherein as an adherent film of substantially even depth which increasesin electrical resistance with depth and is polymerizable thereon byionizing radiation having energy at least equivalent to that of 50,000electron volts, said paint bath, on a pigment and particulatefiller-free basis, comprising an aqueous dispersion of an acidicfilmforming paint binder consisting essentially of a homopolymerizableresin having molecular weight above about 250, at least one dissociablecarboxyl group per molecule and at least 2 units of alpha-beta olefinicunsaturation per molecule,

(2) electrodepositing a film of said binder upon the immersed substrateby employing said substrate as the anode of an electrodeposition celland providing a unidirectional electric current through said dispersionthat is quantitatively and directionally sufficient to effect depositionof a film of said binder upon said substrate by providing a differenceof electrical potential between said substrate and a cathode that is (a)electrically negative in relation to said substrate,

(b) spaced apart from said substrate,

(0) in electrical contact with the aqueous phase of said aqueousdispersion, and

(d) in electrical connection with said substrate in externalrelationship to said bath thereby completing an electrical circuit,

(3) transferring the resultant coated substrate from said aqueousdispersion into a gaseous medium within an irradiation zone,

(4) exposing the electrodeposited film to ionizing radiation in saidirradiation zone in the form of an electron beam having average energyin the range of about 100,000 to about 450,000 electron volts beforesubstantial post deposition dehydration of said film is effected, and

(5) continuing the exposure of said film to said ionizing radiationuntil said film is polymerized on said substrate.

bath.

21. A'method' for coating in accordance 'with claim 19 wherein-saiddifference of electrical potential between said substrate and saidcathode is in the range of about 50 to about 500 volts.

References Cited UNITED STATES PATENTS Gray 204-181 Schmitz et al.1l7-93.31

Marans et al. 117''93.3'1

Anderson 11793.31

20 Livingston et a1. 11793.31 Graham 11793.31 Gilchrist 2041 81 Burlant117-9331 Gentles et al. 204- -181 Hart 204-481 Burlant 1l7-93.31

OTHER REFERENCES Bjorksten et al.: Polyesters and Their Applications,

Reinhold Publishing Corp., New York, 1956, pp. 157 and 158, TP 986 P6B5.

HOWARD S. WILLIAMS, Primary Examiner US. Cl. X.R.

